1. Field of the Invention:
The present invention relates to a reheat type exhaust gas boiler in which superheaters and reheaters are disposed in parallel in the most upstream portion in the direction of exhaust gas flow of an exhaust gas boiler main body.
2. Description of the Prior Art:
Exhaust gas boilers for recovering heat of exhaust gases discharged from various heat generating sources such as gas turbines, diesel engines, cement calcinators or the like are well known and are exemplified by the exhaust gas boiler disclosed in Laid-Open Japanese Patent Specification No. 61-186702 (1986).
A prior art exhaust gas boiler is shown in FIGS. 3 and 4 and includes two sets of secondary superheaters 102 and secondary reheaters 103 disposed in parallel in the most upstream portion in the direction of exhaust gas flow of an exhaust gas boiler main body 101 through which exhaust gas flows longitudinally in the horizontal direction. Primary reheaters 104 are disposed on the downstream sides of the secondary superheaters 102, respectively, and primary super-heaters 105 are disposed on the downstream sides of the secondary reheaters 103, respectively. A high-pressure evaporator 106 is disposed downstream of the primary reheaters 104 and primary superheaters 105 transverse to the direction of exhaust gas flow.
On the downstream side of this high-pressure evaporator 106 is disposed a high-pressure economizer 107, and on the downstream side of this high-pressure economizer 107 are successively disposed a low-pressure superheater 108, a low-pressure evaporator 109 and a low-pressure economizer 110.
A high-pressure steam drum 111 and a low-pressure steam drum 112 are disposed above the exhaust gas boiler main body.
The high-pressure steam drum 111 is connected to an outlet of the high-pressure economizer 107, and also connected to a bottom header 106a of the high-pressure evaporator 106 via a down tube 113. In addition, a top header 106b of the high-pressure evaporator 106 is connected to the high-pressure steam drum 111 via a riser tube 114. Furthermore, a steam section of the high-pressure steam drum 111 is connected to an inlet section of the primary superheater 105 via a steam pipe 115.
Whereas, the low-pressure steam drum 112 is connected to an outlet of the low-pressure economizer 110 and also connected to a bottom header 109a of the low-pressure evaporator 109 via a down tube 116. In addition, a top header 109b of the low pressure evaporator 109 is connected to the low-pressure steam drum 112 via a riser tube 117. Furthermore, the low-pressure steam drum 112 is connected to an inlet side of the high-pressure economizer 107 via a feed water pipe 119 provided with a feed water pump 118. And, a steam section of the low-pressure steam drum 112 is connected to an inlet section of the low-pressure superheater 108 via a steam pipe 120.
In addition, an inlet of the primary reheaters 104 is communicated with a steam turbine not shown through a pipe for returning steam which has done work in the steam turbine. An outlet of the primary reheaters 104 is communicated with the secondary reheaters 103 through a communication pipe not shown. Likewise, an outlet of the primary superheaters 105 is communicated with the secondary superheaters 102 through a communication pipe not shown. And, partition walls 121 are provided between these mutually parallel superheaters and reheaters.
It is to be noted that means for lowering steam temperature are provided midway in the above-described communication pipes and rely upon water spray, water injection or the like to regulate the steam temperature.
The operation of the above-described prior art exhaust gas boiler will now be described.
Exhaust gas discharged from a heat generating source flows into the inlet of the exhaust gas boiler main body 101, is cooled by heat exchange with fluid flowing through heat transfer tubes of the various units 102-110 as it flows about the secondary superheaters 102, the secondary reheaters 103 and through the units 104-110, and flows out through the outlet of the exhaust gas boiler main body 101.
On the other hand, feed water (condensate) is sent to the low-pressure economizer 110 by means of a condensate pump (not shown), and is there heated by the exhaust gas. Then, the heated feed water is sent from the low-pressure economizer 110 to the low-pressure steam drum 112. A part of the feed water in the low-pressure steam drum 112 is sent to the low-pressure evaporator 109 via the down tube 116, is heated in the low-pressure evaporator 109 by the exhaust gas, becomes a fluid mixture of steam and water, and is returned through the riser tube 117 to the low-pressure steam drum 112.
This fluid mixture of steam and water returned to the low-pressure steam drum 112 is separated into steam and water and the steam is sent through the steam pipe 120 to the low-pressure superheater 108, in which the steam is superheated.
Another part of the feed water in the low-pressure steam drum 112 passes through the feed water pipe 119, is boosted in pressure by the pump 118, and is sent to the high-pressure economizer 107. Then, in this high-pressure economizer 107, the feed water is heated by the exhaust gas and sent to the high-pressure steam drum 111. A part of the feed water sent to the high-pressure steam drum 111 is sent to the high-pressure evaporator 106 through the down tube 113, where it is heated by the exhaust gas and becomes a fluid mixture of steam and water, and is returned through the riser tube 114 to the high-pressure steam drum 111.
Within this high-pressure steam drum 111, the fluid mixture is separated into steam and feed water, the steam is sent through the steam pipe 115 to the primary superheaters 105, and in the primary superheaters 105, is superheated by the exhaust gas. Then the superheated steam is sent through the above-described communication pipe to the means for lowering the steam temperature. After the steam has been cooled to a predetermined temperature, it is sent to the secondary super-heaters 102 where high-temperature, high-pressure steam is formed and is sent to the steam turbine.
The steam which has done work in the steam turbine is returned to the primary reheaters 104 where it is superheated. Then, this superheated steam is sent through the above-mentioned communication pipe to the means for lowering the steam temperature, wherein the steam temperature is cooled to a predetermined temperature. The steam is thereafter sent to the secondary reheaters 103 where it is again superheated.
In an exhaust gas boiler having reheaters, it is desirable, in order to effectively carry out recovery of heat from exhaust gas, that the conditions of the exhaust gas be the same as it enters both the superheaters and reheaters and that the conditions of the exhaust gas be the same as it leaves both the superheaters and reheaters. Similarly, it is desirable that the conditions of the steam be the same as it enters both the reheaters and superheaters and that the conditions of the steam be the same as it leaves both the superheaters and reheaters.
To that end, in the prior art, as described above superheaters and reheaters are divided into primary ones and secondary ones. The secondary superheaters 102 and the secondary reheaters 103 are disposed in parallel, the primary reheaters 104 are disposed on the downstream side of the secondary superheaters 102, and the primary superheaters 105 are disposed on the downstream side of the secondary reheaters 103. The primary superheaters 105 and the secondary superheaters 102 communicate with each other, and the primary reheaters 104 and the secondary reheaters 103 communicate with each other. Also, the exhaust gas flow path is divided and the gas flow is guided so as to form proper gas flows by providing partition walls 121 between the respective superheaters and the respective reheaters. In this manner, the gas temperatures immediately downstream of the primary superheaters 105 and the primary reheaters 104 are substantially the same.
The structure of the prior art exhaust gas boiler is, however, complicated due to the fact that the gas path is divided by the partition walls disposed between the superheaters and the reheaters.